- [Instructor] By default, in a switch network,
only a single connection between switches can be active
and forwarding traffic at the same time.
The alternate link will be blocked until the primary fails.
Then it has the opportunity to pass traffic.
This methodology is in place to prevent switching loops.
EtherChannel is an alternative that allows a switch
to simultaneously forward packets across redundant links.
EtherChannel can be referred to as link aggregation group
or bond depending on vendor and product.
The switch will create a logical interface
that is associated with all physical ports
that are part of the EtherChannel.
Within EtherChannel, if a link fails,
there is no STP convergence.
All remaining ports continue to forward traffic.
When a link returns, it will be added back
into the EtherChannel and can begin
forwarding traffic immediately.
Another benefit aside from resiliency, is link capacity.
If two gigabit interfaces are bonded,
the traffic moving across the EtherChannel
can take advantage of the bandwidth with all links combined.
Now to configuration.
Assert with the simplest and not recommended manual method.
First, when you configure an EtherChannel,
you do so with a channel-group command
then verification is done with the show etherchannel command
and then in the output, it will show the term PortChannel.
This is to say they all reference the same thing.
So, keep that in mind.
Using this diagram, I'll configure a bond
between switch one and switch five on ports three and four.
For brevity, I've already configured switch five.
I'll start with the range command.
Config t interface range fa0/ three to four.
The configuration should be completely identical
on these ports, otherwise, it's likely
they won't be added to the bond.
I'll start with a few basics.
Push port trunk encapsulation dot on queue.
Switch port mode trunk.
Now for the me, channel-group one mode set to on.
The channel group number should be the same
on all interfaces that are the part
of the same EtherChannel.
The group number is only locally significant.
Which means the group number
on the adjacent switch can be different.
Go ahead and clear the screen now.
Verification is done with show etherchannel one summary.
This command list all interfaces configured
for the EtherChannel and their associated status.
Here, I see they are listed as P,
which means bundled and port channel.
Also, once the EtherChannel has been added
to the interfaces, a logical port channel interface
is automatically created.
Any subsequent configuration change should be made
directly to the port channel interface.
When a change is made to the port channel interface,
they are automatically added
to the physical interface configurations.
This interface can be viewed just like any other
with show interface, port channel one.
Note that it shows the port numbers.
While manual configuration is simple,
dynamic EtherChannels are their preferred method.
Dynamic uses negotiation of the port
which means it's better at detecting failures
and disabling failing bonded ports.
There are two dynamic EtherChannel protocols.
The Cisco Proprietary Port Aggregation Protocol
and the Standard based Link Aggregation Control Protocol.
While there are differences between the two protocols,
the depths to which I will cover them,
they will essentially be the same.
Each protocol has a mode that will enable
this protocol and start negotiation.
And a mode that will enable this protocol
and wait for the neighbor to begin negotiation.
The basic configuration for either,
is done with the interface configuration
channel group command.
For PAgP, the keyword desirable means enable and negotiate.
While the keyword auto means enable and listen.
For LACP, the keyword active means enable and negotiate
while the keyword passive means enable and listen.
For this example, I'll configure LACP
since they both configure almost identically.
Switch five has been pre-configured for LACP
on ports three and four, so I'll complete
the configuration on switch one.
Config space t, interface range fa0/ three to four,
switch port trunk encapsulation dot on queue.
Switch board mode trunk.
Now, channel-group one mode active.
I'll go ahead and clear this screen for verification.
Verification is done view show etherchannel
one port channel.
This will list the protocol in use
along with with the state of each port.
As useful as EtherChannels are for layer two networks,
they can also be used for layer three connections.
This can be layer three switch to layer three switch,
it can be layer three switch to router
or router to router.
In this case, I'll continue using the same switches
but configure their bond and interfaces
to be layer three interfaces.
Again, switch five is preconfigured,
so I'll do the configuration on switch one and test.
Again, I'll start with a range command.
Config t interface range fa0/ three to four.
Now, I'm going to turn off the switch port.
No switch port.
Next, I'll enable the channel group.
Channel-group and mode active.
This enables LACP.
Using the no switch port command
makes the interfaces routed.
And now I'll assign an IP address
to the logical port channel interface.
Interface po one and ip address,
192.168.1.1 with a subnet mask of 255.255.255.0.
I'll wait for the interface to come up.
And then I'll clear the screen for some verification.
We'll do a simple ping test to switch five.
Ping 192.168.1.2.
Success.
I use EtherChannels quite frequently
at mission critical locations.
While the increase bandwidth is nice,
it can be a simple and reliable way
to add resiliency into the network.